Photometric Surveys of Suspected Small-Amplitude Red Variables. III. An AAVSO Photometric Photometry Survey

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1 Publications of the Astronomical Society of the Pacific 106: , 1994 June Photometric Surveys of Suspected Small-Amplitude Red Variables. III. An AAVSO Photometric Photometry Survey John R. Percy and Nancy Wong Erindale Campus, University of Toronoto, Mississauga, Ontario L5L 1C6, Canada Electronic mail: Dietmar Bohme Nr. 11, PSF 93, Nessa 04851, Germany David R. Curott Lioncrest Observatory, Department of Physics and Earth Science, University of North Alabama, Florence, Alabama Frank Dempsey 1152 Tänzer Court, Pickering, Ontario L1W 3S6, Canada George L. Fortier 63 Devon Road, Baie d Urfe, Quebec H9X 2W7, Canada Matt Ganis and Stephanie Parello Pace Observatory, 861 Bedford Road, Pleasantville, New York Howard J. Landis Landis Observatory, 303 Saddle Creek Drive, McDonough, Georgia Kenneth D Giddings Avenue NE, Albuquerque, New Mexico Donald Furnace Hill Observatory, 40 Hillcrest Drive, Cranston, Rhode Island Michael S North Table Mountain Road, Tucson, Arizona Leroy F. MacLean Observatory, P. O. Box 3964, Incline Village, Nevada Raymond R. 7 Welton Street, Maple, Ontario L6A 1R8, Canada Rick Wasson Sunset Hills Observatory, Del Prado Drive, Hacienda Heights, California Harold O. Williams and William S. G. Walker Williams Observatory, 71 Milton Road, Mt. Eden, Auckland 4, New Zealand James E. Faun Lane Observatory, Faun Lane, Garden Grove, California (Received 1993 September 23; accepted 1994 March 9) ABSTRACT. We have carried out a survey of the photometric (V) variability of 61 known or suspected small-amplitude red variables, mostly M giants. Approximately two-thirds appear to be variable; several suspected variable comparison stars have also been identified. The incidence and average amplitude of variability increase rapidly from spectral type M0 III to M6 III Astronomical Society of the Pacific

2 612 PERCY ET AL. 1. INTRODUCTION Small-amplitude red variables (SARVs) are M giants that are pulsating with small amplitudes and with periods of up to 200 days. Most of the known SARVs are bright stars. There are 164 known and 136 suspected variables among the approximately 500 M giants in the Yale Catalogue of Bright Stars (YCBS). There are also 16 known and 215 suspected variables among the approximately 1600 K giants in that catalog. Very few of these are actually variable; those which are appear to be RS Canum Venaticorum stars (Percy 1993). SARVs are red-giant or asymptotic-giant-branch stars. Their properties have been reviewed by Querci (1986) and Percy (1985). A detailed study of a typical SARV (EU Delphini) has been reported by Percy et al. (1989). As a long-term project, one of us (J. R. P.) is accumulating and analyzing observations of SARVs using a variety of techniques and sources. The goal is to clarify the status of the many hundred suspected or poorly documented SARVs in the YCBS, as well as to understand the systematics, evolutionary status, pulsation properties, and processes in these stars. Part of the survey has been carried out with the 0.4-m teaching telescope on the main campus of the University of Toronto (Percy and Fleming 1991; Percy and Shepherd 1992). Another part (reported here) has been carried out through the photoelectric photometry program of the American Association of Variable Star Observers (AAVSO). 2. OBSERVATIONS Program stars were observed in the V band, relative to comparison and check stars of mostly G and K type (since other M giants would be likely to be variable). The differential observations were corrected for extinction, and transformed to the standard UBV system, either by a standard procedure at AAVSO HQ or by individual observers using a similar procedure. The accuracy of the observations varies with both the individual observer, and with the differential brightness, color, and air mass of the stars involved. Typical accuracies are given in square brackets below. Note that, since each star was observed by one observer only, there were no errors due to systematic differences between observers. The observers equipment was as follows. Böhme [0.010]: Hopkins Observatory photometer on a 25 cm Cassegrain; Curott [0.010]: OPTEC SSP-5 on a 25 cm Meade cassegrain; Dempsey [0.012]: SSP-3 on a 15 cm Newtonian; Fortier [0.010]: OPTEC SSP-3 on a 32 cm Newtonian; Ganis/Parello [0.012]: Starlight-1 on a 28 cm (11") Celestron; Landis [0.008]: homebuilt photometer (1P21 PMT) on a 20 cm Newtonian; [0.012]: SSP-3 on a 20 cm (8") Celestron; [0.010]: SSP-3 on a 25 cm Meade cassegrain; [0.012]: SSP-3 on a 20 cm (8") Celestron; [0.008]: SSP-3 on a 56 cm (22") cassegrain; [0.010]: SSP-3 on either an 11 cm polar axis refractor or a 25 cm Schmidt-cassegrain; Wasson [0.012]: SSP-3 A on a 36 cm Newtonian; [0.010]: homebuilt photometer (EMI 9924A PMT) on a 53 cm cassegrain; [0.012]: SSP-3 on a 25 cm Schmidt-cassegrain. 3. RESULTS The results are summarized in Table 1, which gives the basic information on the program, comparison, and check stars; for the program and check stars, it gives the mean AV relative to the comparison star, the standard deviation, number of observations, and an assessment of the variability. Generally, stars were considered to be variable if <x>0.020; probably constant if 0.015^ct<0.020, and constant otherwise. GCVS4 refers to the Fourth Edition of the General Catalogue of Variable Stars (Kholopov 1985). NSV refers to the New Catalogue of Suspected Variable Star (Kholopov 1982). Notes on individual stars are given below, and a few representative light curves are shown in Figs NOTES ON INDIVIDUAL STARS HR Scl; Lb variable, range 4.80 to 4.90 in V (GCVS4). We find 4.79 to 4.96 and a time scale of a month or two; the observations are sparse. HR 257. BQ Tue; Lb? variable, range 5.60 to 5.80 (GCVS4). We find 5.62 to 5.82 and a time scale of a month or two; the observations are sparse. HR 304. CC Tue; range 0.10 in V (GCVS4). We find 6.24 to 6.34 and a time scale of 25 days. HR 689. VAR? (YCBS). We find 5.23 to 5.30; the time scale may be about 20 days. HR BQ Gem; SRb variable, range 6.63 to 7.02 in B, time scale about 50 days (GCVS4). We find 4.84 to 5.26 in V and periods of 52 days and possibly a year or more (Fig. 1). HR NZ Gem; SR variable with a range of 5.52 to 5.72 in V (GCVS4). We find 5.50 to 5.61 and a rather irregular light curve with time scales of 40 and >200 days. HR BC CMi; SRb variable, range 6.14 to 6.42 in V, time scale about 35 days (GCVS4). We find 6.16 to 6.40 and a similar time scale. HR BL Cnc; Lb variable, range 5.97 to 6.04 (GCVS4). We find 5.87 to 6.07 and a rather irregular light curve with time scales of 20 and >100 days (Fig. 2). HR BP Cnc; SRb variable, range 5.41 to 5.75, period about 40 days. (GCVS4). We find 5.43 to 5.75 and a period of 40 days (Fig. 3). HR NSV (variability doubtful). We find a range of 6.30 to 6.39; the time scale is uncertain. HR NSV 04514; range 4.28 to 4.34 in V. There is one discordant observation; otherwise the range is ^0.02. HR NSV 04764; variable in K magnitude. We find a range of 5.79 to 5.88 and a time scale of 30 days. HR U UMa, range 6.20 to 6.25 in V (GCVS4); constant? (YCBS). We find a range of 6.13 to 6.19 and a time scale of a month or two. HR RX LMi; SRb variable, range 5.98 to 6.16, period 150: days (GCVS4). We find 5.99 to 6.08 and a possible short time scale as well as a longer (>100 days) one. HR VY Leo; Lb? variable; range 5.69 to 6.03 (GCVS4). We find 5.77 to 6.14, and time scales ranging from 40 days to a year or more. HR o) Vir; Lb variable, range 5.23 to 5.50 (GCVS4). We find 5.23 to 5.37, with time scales of 30 to >100 days.

3 AAVSO PHOTOELECTRIC PHOTOMETRY SURVEY 613 Table 1 Results of a Survey of the Photometric Variability of a Sample of Suspected Small-Amplitude Red Variables Program Star HR V B-V SpT AV N R ,57 M2III c? ,64 M4III ,56 M4III M2III ,65 M2III v ,.77 M4III v M2II c? M4III v M1III ,63 M1III c 2795,52 MOIII c? ,54 MOIII c ,64 M3II-III ,59 M4III ,66 M3III v ,60 M3III v M3III c M4III v K7III ,53 MIHI c K5III ,63 M2III ,,29 gk MOOOO v ,,20 K2III c ,62 M2III ,.45 M5.5III v ,57 M2III c ,.57 M4III v M1III c? M3III c ,.60 M3III c? M1III c M5III ,.73 M2III v M6III v M2.5III c? M3III M4III M3III v M5III v K2III c M4III M4III M1III v M2III M4III M3III v K0III gk c M3III v M1III c G6-8III c M4.5III c? M4III v M3III M5III M1III M2III M3III M2.5III v Check Star HR V B-V SpT AV N R K0III c? K1III v G1V c K5III c gg v K0III c '+1.45 K3I-II c G8III v G4V c G4V v G9V v G8III c? K v K1III : K1III-IV c : G8III v , G6III c , G1V c? , G8III G8III c , KOIII v : MOIII c F6V v , F9V c K3III gg K4III K5III A4V A4V c K). 01 A1V A1V K5III c K4III G8III v G8III KOIII F6III F7V KOIII G8III F5V F5V K1III F2V K5II M1III G1V K1III F0V G8III G8III K4III F7V : M1III G4V K3III K3III M2III v c c? v c v c v c? c c? v? v c v Comparison Star HR V B-V SpT 22, G9III 35, F4V 186, K5III 270, K2III GO.5IV K0 1129, G0III : ggl G8III G8III F5V 2985, G8III : K0 3093, G8III GiV 3376, KOIII 3609, K5III K1III G8.5III gg ,, K2III , gk , gk ,, gk gk , K1III , gkl K2III gko , gko gk gk KOIII F9IV KOIII B gk K3-4III gko KOIII gkl : K ,64 K4III K4III KOIII G5-8III K3V K2III F5V KOIII G5III KOIII KOIII KOIII G3IV G8V : G9III F4V G7III G7III M2III Observer Curott Fortier Wasson Landis Fortier Curott Wasson Dempsey Bohme Dempsey Ganis Kuedeke HR RR UMi; SRb variable, range 4.53 to 4.73 in V, period 43.3 days (GCVS4). We find 4.33 to 4.68 in V, and a time scale ranging from 30 to 50 days. HR NSV 07574, range 4.9 to 5.47 in V. We find 5.38 to 5.54; the time scale is uncertain. HR g Her; SRb, range 4.3 to 6.3 in V, period 89.2 days (GCVS4). We find 4.57 to 5.46, and a time scale of 80 to 90 days. The light curve is semiregular. HR VAR? (YCBS). We find a range of 5.79 to 5.91; the time scale is uncertain. HR V642 Her; SRb variable, range 6.41 to 6.56, time scale about 12 days (GCVS4). We find 6.32 to 6.55, and a time scale of 25 days (Fig. 4). HR V669 Her; range 0.14 (GCVS4). We find 4.88 to 5.00 in V; the time scale is uncertain, but may be about 20 days. HR V4028 Sgr, SR: variable, range 6.10 to 6.38 in V; time scale 35: days (GCVS4). We find a range of 6.06 to 6.30, and a time scale of >50 days. HR V3879 Sgr; SRb variable, range 6.05 to 6.58, time scale about 50 days (GCVS4). We find 6.30 to 6.57 and a time scale 50 days from sparse data.

4 614 PERCY ET AL. HR 3319 JULIAN DATE ( ) Fig. 1 The V light curve of BQ Gem (HR2717), relative to the comparison star HR The line segments have been added to delineate the variations, which have a time scale of 52 days. There is some evidence for longer-term variations. The error bar is shown in the upper left comer. Fig. 3 The V light curve of BP Cnc (HR 3319), relative to the comparison star HR The line segments have been added to delineate the variations, which have a time scale of 40 days. The error bar is shown in the upper left comer. HR VAR? No NSV number; range 0.15 in V (YCBS). We find 6.30 to 6.45 and a time scale of 50 days, from sparse data. HR NSV 12432, range 0.12 in V. We find 5.85 to 5.91; the time scale is uncertain. HR V1509 Cyg; Lb variable, range 5.08 to 5.4 in V (GCVS4). We find 5.15 to 5.31, and a time scale of 30 days. The observer did not use a check star. HR NSV (but variability doubtful). We find a range of 6.18 to 6.42, and a time scale of 50 days. HR EN Aqr; Lb variable, range 4.41 to 4.45 (GCVS4). We find 4.14 to 4.49, with a time scale of about 30 days. HR This variable Ml III check star is presumably a HR NSV 13729, range 6.09 to 6.5 in V. We find a range of 6.08 to 6.16, and a time scale of about 25 days. HR 3169 HR v Tue. Lb: variable, range 4.75 to 4.93 (GCVS4). We find a range of 4.77 to 4.88; the time scale is uncertain. HR NSV 14529, range 0.14 in V. We find 6.03 to 6.11; the time scale is uncertain. HR This variable Ml III check star is presumably a HR This variable M2 III check star is presumably a 5. DISCUSSION AND CONCLUSIONS Our results confirm the variability of many known or suspected SARVs, and identify several new variables. These will be followed up on a long-term basis as part of the AAVSO photoelectric photometry program. Such a program HR 6543 Fig. 2 The V light curve of BL Cnc (HR 3169), relative to the comparison star HR The line segments have been added to delineate the variations, which appear to have time scales of about 20 and >100 days. The error bar is shown in the upper left comer. Fig. A (a) and (b) The V light curve of V642 Her (HR 6543), relative to the comparison star HR 6542, over two seasons. The line segments have been added to delineate the variations, which have a time scale of 25 days; there is some evidence for longer-term variations. The error bar is shown in the upper left comer.

5 AAVSO PHOTOELECTRIC PHOTOMETRY SURVEY 615 Fig. 5 The amplitude of variation in V, as a function of the published spectral type. Since the data are sparse, and the amplitude may be variable with time, this graph shows a general trend only. has proven to be effective in discovering or confirming the variability of these stars, and in following them up. Figure 5 summarizes the results: the incidence of amplitude of variability become noticeable at about Ml III spectral type, and tend to increase with advancing spectral type. The trend, however, is not an exact one. Several of the stars show some evidence of variability on both short time scales (weeks) and long time scales of a year or more. This is a characteristic of many SARVs (Percy et al. 1993). Many years of observations will be required in order to identify the periods. The long-term variability is of particular interest, because its cause is not known. We thank Howard J. Landis for his many contributions to the AAVSO photoelectric photometry program, and Janet A. Mattei for her interest and cooperation. J. R. P. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada in the form of a research grant. REFERENCES Kholopov, P. N. (editor-in-chief) 1982, New Catalogue of Suspected Variable Stars (Moscow, Nauka) Kholopov, P. N. (editor-in-chief) 1985, General Catalogue of Variable Stars, Fourth ed. (Moscow, Nauka) Percy, J. R. 1985, IAPPP Commun., 19, 14 Percy, J. R. 1993, PASP, 105, 1422 Percy, J. R., Landis, H. J., and Milton, R. E. 1989, PASP, 101, 893 Percy, J. R., and Fleming, D. E. B. 1991, PASP, 104, 96 Percy, J. R, and Shepherd, C. W. 1992, IAU Inf. Bull. Var. Stars, No Percy, J. R., Ralli, J. A., and Sen, L. V. 1993, PASP, 105, 287 Querci, F. R. 1986, in The M-Type Stars, ed. H. R. Johnson and F. R. Querci (Washington, NASA SP-492)